08.11.08: The Information Cycle


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08.11.08: The Information Cycle

  1. 1. Author(s): Rajesh Mangrulkar, MD, 2009License: Unless otherwise noted, this material is made available under the terms ofthe Creative Commons Attribution–Non-commercial–Share Alike 3.0 License:http://creativecommons.org/licenses/by-nc-sa/3.0/We have reviewed this material in accordance with U.S. Copyright Law and have tried to maximize your ability to use, share, andadapt it. The citation key on the following slide provides information about how you may share and adapt this material.Copyright holders of content included in this material should contact open.michigan@umich.edu with any questions, corrections, orclarification regarding the use of content.For more information about how to cite these materials visit http://open.umich.edu/education/about/terms-of-use.Any medical information in this material is intended to inform and educate and is not a tool for self-diagnosis or a replacement formedical evaluation, advice, diagnosis or treatment by a healthcare professional. Please speak to your physician if you have questionsabout your medical condition.Viewer discretion is advised: Some medical content is graphic and may not be suitable for all viewers.
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  3. 3. Patients and Populations Medical Decision-Making: The Information Cycle Rajesh S. Mangrulkar, M.D.Fall 2008
  4. 4. A Clinical Tale•  20 year-old woman presents for genetic testing•  Mother had breast and ovarian cancer, likely has the BRCA gene (autosomal dominant)•  With this assumption, the patient s likelihood of having the gene is… 50%•  She decides not to get tested.
  5. 5. The Tale Continues…FFwd•  At age 75 she has not been diagnosed with breast or ovarian cancer.•  Is her probability of having the BRCA gene different at age 75 than it was at age 20? –  Yes: it is lower –  How much lower?
  6. 6. Diagnostic Reasoning: Probabilistic ReasoningProbability: The likelihood of the occurrence of an event.•  P (X) = the probability of event X•  P(BRCA) = the probability that a patient carries the BRCA gene
  7. 7. Prior Probabilities•  Based on many factors: –  Clinician experience –  Patient demographics –  Characteristics of the patient presentations (history and physical exam) –  Previous testing –  Genetic knowledge (in this case)•  P(BRCA) = 50%
  8. 8. Conditional Probabilities•  What is the probability of event B, given an event A? Written as P(B | A). –  Example: P (BRCA | no breast cancer)•  Key concept: –  Conditional probabilities can be combined with prior probabilities to create joint probabilities
  9. 9. Basic Probabilistic Rules Examples of types of Events•  Dependent events: occurrence of 1 depends to some extent on the other –  Example: The same person passing step 1 of the boards and then passing step 2 of the boards 2 years later.•  Independent events: both can occur –  Example: 2 different people passing step 1 of the boards•  Mutually exclusive events: cannot both occur –  Example: A person getting >250 on step 1 of the boards, or the same person getting 220-250 on step 1.
  10. 10. Combining Probabilities of Events•  Pr (A B) = Pr (A) + Pr (B) –  If A and B are mutually exclusive events•  Pr (A B) = Pr (A) * Pr (B) –  If A and B are independent events•  Pr (A B) = Pr (A) * Pr (B|A) –  If A and B are dependent events (Joint probability) = OR = AND
  11. 11. Back to our story75 yo woman whose mother very likely had the BRCA gene, but who has not herself been diagnosed with breast cancer.•  Our patient wants to know: –  What is P (BRCA | no breast ca)?
  12. 12. Considering both sides…•  Step 1: P (BRCA and no breast cancer) = P(BRCA) * P(no breast ca | BRCA) = 0.5 * 0.3 (from studies) = 0.15•  Step 2: P (NO BRCA and no breast ca) = P(NO BRCA)*P(no breast ca|NO BRCA) = 0.5 * 0.875(from studies) = 0.4375
  13. 13. But that doesn t tell the full story…•  Joint probabilities –  P (BRCA and no breast ca) = 0.15 –  P (NO BRCA and no breast ca) = 0.4375•  The assumption is that these are NOT independent events.•  Again, our patient wants to know: –  What is P (BRCA | no breast ca)?
  15. 15. Step 3: Bayes Theorem•  Conditional probability is the relative proportion of the relevant joint probability to the sum of all the joint probabilities.•  P(BRCA | no breast ca) = P(BRCA) * P (no breast ca | BRCA) P (no breast ca)•  P (no breast ca) = sum of all the joint probabilities •  P (no breast ca & BRCA) •  P (no breast ca & NOT BRCA)
  16. 16. Applying Bayes Theorem•  P (BRCA | no breast ca) = 0.15 ------------------- = 26% 0.15 + 0.4375•  26% is significantly lower than 50% (our prior probability)
  17. 17. Why is this important?•  Illustration of changing probabilities, and shifting uncertainty… …because of test results …because of events …because of time•  Fundamentally, clinicians deal with probabilities and uncertainty with each patient they encounter
  18. 18. Final tale: Diagnostic Reasoning•  The case: A 56 year old man without heart disease presents with sudden onset of shortness of breath.•  Description of the problem: Yesterday, after flying in from California the day before, the patient awoke at 3AM with sudden shortness of breath. His breathing is not worsened while lying down.
  19. 19. Diagnostic Reasoning: Your Intake•  Q: What other symptoms were you feeling at the time?•  A: He has had no chest pain, no leg pain, no swelling. He just returned yesterday from a long plane ride. He has no history of this problem before. He takes an aspirin every day. He smokes a pack of cigarettes a day.
  20. 20. Diagnostic Reasoning: Baby StepsPrior to Lectures on 8/18…•  What are you thinking may be going on at this time? In other words, generate a differential diagnosis of possibilities…•  Assign likelihoods to each possibility•  Place the possibilities in descending order of likelihood
  21. 21. Thread 1: Information Retrieval Ask Acquire Apply Appraise R. Mangrulkar
  22. 22. Riddle me this...•  How many questions do clinicians ask while they care for patients? 4 per patient•  How can knowledge of question structure improve the efficiency of the information retrieved? (1) Targeting Information Resources (2) Generating Search Terms
  23. 23. Research: Questions New Knowledge Early Hypothesis (Basic Science theory, case reports, cross-sectional studies) Mature Hypothesis (Consistent support from observational studies) Confirm Causal Link (Large prospective randomized trials) Optimal Decision Making (Use information on treatment benefit, risks and costs from trials and observational studies, simulation models)R. Mangrulkar
  24. 24. Objectives of today s session•  By the end of this lecture, you should be able to… –  demonstrate an understanding of the difference between background and foreground clinical questions –  appreciate how individual targeted searches for the answers to clinical questions drive self- directed learning that is crucial for all practitioners –  be able to craft foreground questions for both diagnosis and treatment, using the PICO format
  25. 25. Patient Care: Questions Decisions•  Step 1: Question Search for Answer•  Step 2: Assess the strength of answer•  Step 3: Weigh against: –  Patient Values –  Physician Values –  Society s Values
  26. 26. A Tale: The Concierge•  The case: You and your friend are at the Drake Hotel in Chicago, and need to find a place to eat for dinner.•  Description: You both are vegetarian. You are both in the mood for Asian cuisine. You only have 2 hours to eat, so you don t want to take a cab, car or train. You both are on a tight budget so entrees should not be expensive.
  27. 27. The Concierge: Scenario #1 •  Q: Could you suggest a place for my friend and I to eat close by? •  A: What kind of restaurant? •  Q: Well, it should be around here. •  A: We have dozens of excellent restaurants close to the Drake. •  Q: Yeah, one of those… •  A: Can you be more specific? •  Q: Well, we re kind of in a hurry so it should be close by...
  28. 28. The Concierge: Scenario #2•  Q: Can you help us find a restaurant?•  A: Sure. What are you looking for?•  Q: Well, we re in the mood for Thai cuisine with an excellent vegetarian selection. It should be walking distance from here, with a nice view of the city. Not too pricey, say $15 per entrée.•  A: Ah! I have the perfect place…Thai Peppers. Let me call ahead and let them know you ll be coming.
  29. 29. What makes a good question?•  #1: Could you suggest a •  #2: Can you help us find place for my friend a vegetarian Thai and I to eat close by? restaurant, walking distance from here, about $15 per entrée?What aspects of the second question predicted its success at retrieving a place that the customers were satisfied with?
  30. 30. The Well-Structured Clinical Question•  Purposes –  Target resources –  Define search terms –  Define what you and the patient care about•  Two Types –  Background –  Foreground
  31. 31. Anatomy of a Background Question •  What •  How •  Where •  When •  Who •  Why
  32. 32. 54/67 (81%) of allquestions posedby the Riddler were The RiddlerBackground-type How much dirt is in a hole 3 acres square and 200 None, because its a hole feet deep? What has neither flesh, bone, nor nail yet has 4 A glove fingers and a thumb? When is the top of a mountain like a savings When it peaks ones interest account? A bear lumbers and a fallen tree Why is a bear like a fallen tree? becomes lumber Which president wears the largest hat? The one with the biggest head
  33. 33. Anatomy of a Background Question •  What •  Disorder •  How •  Syndrome •  Where •  Finding •  When •  Health state •  Who •  Concern •  Why
  34. 34. Background Questions -- Examples•  Who should get influenza vaccine and when?•  Which drugs to treat HIV can cause pancreatitis?•  What is the metabolic pathway for cholesterol synthesis?•  Why do patients with sleep apnea have high blood pressure?
  35. 35. Background vs. Foreground Questions•  Background: Designed to improve general knowledge about a subject•  Foreground: Patient-specific questions, strong implications for decisions, often with comparisons
  36. 36. An Evolution in Question Type100 90 80 70 60 Foreground 50 Background 40 30 20 10 0 M1-M2 M3-M4 Residency PracticeR. Mangrulkar
  37. 37. Background vs. Foreground Questions•  Background: Designed to improve general knowledge about a subject•  Foreground: Patient-specific questions, strong implications for decisions, often with comparisons
  38. 38. Background Questions: A CaseUsing the following case, jot down 3 questions with your partner that may help you care for this patient:A 42 year old woman comes to her primary care practitioner s office for follow up of her diabetes. She is currently on glyburide 10 mg twice daily. However, her morning and evening blood sugars still stay elevated. You are the medical student who sees this patient with your attending. Afterwards, your attending asks whether you think she should add metformin to her regimen. You say that you don t know because your knowledge of diabetes medications are sketchy.
  39. 39. Background Questions•  What kind of medication is glyburide?•  In what classes of medication do metformin and glyburide fall?•  What is the initial dosage of metformin?•  What are the adverse effects of metformin that I must be cautious about?•  Is it safe to be on glyburide and metformin at the same time?
  40. 40. Sources for Background Questions•  Course notes, lectures, syllabi•  Textbooks –  MD Consult –  Stat!Ref –  Up-To-Date•  Review articles•  Practice Guidelines
  41. 41. Background vs. Foreground Questions•  Background: Designed to improve general knowledge about a subject•  Foreground: Patient-specific questions, strong implications for decisions, often with comparisons
  42. 42. Foreground Questions -- Examples•  In patients with chronic •  In patients with acute atrial fibrillation over the chest pain of less than 6 age of 70, does warfarin hours duration, what is anticoagulation reduce the diagnostic accuracy the rate of stroke and of a single troponin level death when compared when compared with with aspirin? serial EKG s and enzymes? Therapy Diagnosis
  43. 43. Foreground Questions -- ExamplesTherapy•  In patients with chronic atrial fibrillation over the age of 70, does warfarin anticoagulation reduce the rate of stroke and death when compared with aspirin?Diagnosis•  In patients with acute chest pain of less than 6 hours duration, what is the diagnostic accuracy of a single troponin level when compared with serial EKG s and enzymes?
  44. 44. PICO: A Tool to Structure the Foreground Question Therapy DiagnosisP Patient Pop DiseaseI Intervention TestC Comparison Gold StandardO Outcome Accuracy
  45. 45. Foreground Questions - CaseUsing the PICO model, jot down 1 foreground question with your partner that will help you care for this patient:A 42 year old woman comes to her primary care practitioner s office for follow up of her diabetes. She is currently on glyburide 10 mg twice daily. However, her blood sugars still stay elevated. After you see this patient, your attending asks whether you think she should add metformin to her regimen.Patient - Intervention - Comparison - Outcome
  46. 46. Foreground Questions - Therapy•  In type II diabetics, is metformin and glyburide better than glyburide alone at lowering blood sugar?•  Among women with type II diabetes, are there more instances of low blood sugar events in patients on both metformin and glyburide, compared to glyburide alone?
  47. 47. Sources for Foreground Questions•  MEDLINE•  Practice Guidelines•  Evidence Based-Databases –  Cochrane Library –  ACP Journal Club
  48. 48. Additional Source Information for more information see: http://open.umich.edu/wiki/CitationPolicySlide 21: Rajesh MangrulkarSlide 23: Rajesh MangrulkarSlide 36: Rajesh Mangrulkar